The present invention relates to pulse code modulation (PCM) networks such as communications systems, in which operational signals are transmitted along with the voice and/or data signals. The operational signals are binary coded patterns and serve various functions such as start and stop for billing purposes and other administrative functions. This non-voice binary communication is called signaling.
At the present time, the signaling is done by different signaling systems in various types of PCM networks. However, the per channel bandwidth of these signaling systems is fixed at 4 bits every 3 ms. The different signaling systems have signaling rates determined by the number of bits in the binary signaling patterns and the period with which those patterns are repeated One type of binary signaling pattern in general use is the ABCD pattern which transmits the signaling information in four-bit patterns repeating every 3.0 ms and consequently has a signaling rate of 333 Hz. Two bit patterns repeating every 1.5 ms are used by some systems and are known as AB patterns with a rate of 667 Hz. Another type of signaling pattern is the A pattern being a single bit pattern repeating every 0.750 ms and having a rate of 1333 Hz. Networks using these various signaling patterns are commonly referred to as A, AB, or ABCD networks.
It regularly occurs that a network of higher signaling rate connects to a network using a lower signaling rate and vice versa. In some instances the interface between the higher signaling rate network and an ABCD network can result in signal patterns being mapped into the ABCD network which can adversely affect network operation and the transparent transport of signaling information. The present invention is concerned with selective or controlled mapping of one signaling rate network into another signaling rate network at an interface.
In addition to the voice and data signals and the binary coded operational signals, it is usual to have certain designated ABCD network patterns reserved for network specific functions. One of these reserved non-signaling patterns are in one instance referred to as the Unicode pattern.
The invention will be described with respect to a particular type of problem that occurs at a signaling rate conversion boundary or interface when a higher signaling rate network interfaces an ABCD signaling rate network. The problem results from the fact that the higher rate pattern can be repeated more than once during the time needed for an ABCD pattern and depending upon the phase of the mapping ambiguous, redundant patterns can be produced in the ABCD network. In most cases these ambiguous, redundant patterns do not provide a serious problem. However, in certain situations the ambiguous, redundant patterns can result in erroneous network operation as when one of these redundant pattern mappings is the same as a reserved network specific pattern such as Unicode. It is to this general problem that the present invention is directed.
This compatibility problem exists at certain PCM interfaces and jeopardizes the error free transport of signaling information the error-free transport of voice information, the error-free transport of data information and correct telecommunications network operation. Non-signaling, network specific ABCD patterns, such as Unicode which have been defined in ABCD networks may be erroneously introduced into an ABCD network at these signaling rate changing interfaces. This can cause signaling, voice, and data information blockage and incorrect operation of the ABCD network.
For example, the ABCD Unicode pattern 0010 which is used in some networks may be falsely introduced at AB to ABCD signaling rate conversion interfaces. This is particularly so when certain AB signaling states defined in Bellcore Technical Requirement TR-TSY-000008 are mapped into an ABCD network. This can cause untimely trunk conditioning in the ABCD signaling system where Unicode is defined at the downstream termination from where this translation occurs and can prevent the correct AB signaling state from being delivered to its destination.
When higher rate AB signaling is uncontrollably mapped into an ABCD network the full complement of ABCD patterns available in the ABCD network cannot be freely used due to the redundant ABCD patterns that can be produced when AB signaling is mapped into an ABCD network.